Conventionally, an inverter that includes two metal-oxide semiconductor field-effect transistors (MOSFETs) coupled in series between a direct current (DC) power supply and a ground is known, for example, as disclosed in TOSHIBA REVIEW, Vol. 61, No. 11, p. 32 (2006) (hereafter, referred to as Nonpatent Document No. 1). To a middle point between the two MOSFETs, an inductive load is coupled. The MOSFETs include parasitic diodes. Thus, in the inverter, two switching elements are coupled in series between the DC power supply and the ground, and the parasitic diodes are coupled in inverse-parallel with the switching elements, respectively. The inverter alternately turns on the two switching elements (MOSFETs) with a dead time during which both the two switching elements are turned off.
In cases where electric current flows into the inductive load and electric current flows into the parasitic diode in the dead time, carries are stored in the parasitic diode into which the electric current flows. When the other switching elements is turned on from the above-described state, a recovery current flows to the parasitic diode and ringing occurs in voltage between both ends of the parasitic diode. The ringing is a LC resonance depending on a capacitance of the parasitic diode and a parasitic inductive load of the inverter. A magnitude of the ringing depends on the carriers stored in the parasitic diode.
In order to restrict generation of the ringing, the inverter disclosed in the Nonpatent Document No. 1 includes recovery assist circuits coupled in parallel with the MOSFET. The recovery assist circuit includes a recovery assist switch circuit and a recovery assist auxiliary power supply coupled in series. In the dead time, when the recovery assist switch circuit is turned on, a voltage of the recovery assist auxiliary power supply is applied to the parasitic diode in the reverse direction. Accordingly, storage of the carriers is restricted, and the ringing is restricted.
As described above, the inverter disclosed in the Nonpatent Document No. 1 includes the recovery assist circuit coupled in parallel with the MOSFET, and the recovery assist circuit includes the recovery assist auxiliary power supply. Because the recovery assist auxiliary power supply is used in addition to the DC power supply, a dimension and a cost of the inverter increase.